diff --git a/pkg/agent/agent_test.go b/pkg/agent/agent_test.go
index 4047ab74d..3636e6c78 100644
--- a/pkg/agent/agent_test.go
+++ b/pkg/agent/agent_test.go
@@ -266,6 +266,85 @@ func TestProcessMessage_IncludesCurrentSenderInDynamicContext(t *testing.T) {
 	}
 }
 
+// TestProcessMessage_AttachesSenderAttributionToUserMessage exercises the
+// end-to-end flow for issue #2702: a real-user inbound message reaches
+// the provider with a sanitized Name field so multi-user conversations
+// can be disambiguated by the model. The sanitization step is what makes
+// the value safe for OpenAI's `name` constraint (`^[a-zA-Z0-9_-]{1,64}$`).
+func TestProcessMessage_AttachesSenderAttributionToUserMessage(t *testing.T) {
+	tmpDir := t.TempDir()
+	cfg := &config.Config{
+		Agents: config.AgentsConfig{
+			Defaults: config.AgentDefaults{
+				Workspace:         tmpDir,
+				ModelName:         "test-model",
+				MaxTokens:         4096,
+				MaxToolIterations: 10,
+			},
+		},
+	}
+	msgBus := bus.NewMessageBus()
+	provider := &recordingProvider{}
+	al := NewAgentLoop(cfg, msgBus, provider)
+
+	if _, err := al.processMessage(context.Background(), testInboundMessage(bus.InboundMessage{
+		Channel:  "discord",
+		SenderID: "discord:123",
+		Sender:   bus.SenderInfo{DisplayName: "Alice"},
+		ChatID:   "group-1",
+		Content:  "My name is Alice",
+	})); err != nil {
+		t.Fatalf("processMessage(): %v", err)
+	}
+
+	if len(provider.lastMessages) == 0 {
+		t.Fatal("provider received no messages")
+	}
+	last := provider.lastMessages[len(provider.lastMessages)-1]
+	if last.Role != "user" || last.Content != "My name is Alice" {
+		t.Fatalf("last message = %+v, want user/My name is Alice", last)
+	}
+	// "discord:123" → "discord_123" (colon disallowed in OpenAI name).
+	if last.Name != "discord_123" {
+		t.Errorf("last.Name = %q, want discord_123 (sanitized)", last.Name)
+	}
+}
+
+// TestProcessMessage_NoSenderAttributionForCronTrigger verifies that
+// synthetic trigger sources (cron/heartbeat/async callbacks) do not
+// produce per-message sender attribution. Otherwise an Anthropic adapter
+// would render `[cron] [System: cron] ...` double prefixes.
+func TestProcessMessage_NoSenderAttributionForCronTrigger(t *testing.T) {
+	tmpDir := t.TempDir()
+	cfg := &config.Config{
+		Agents: config.AgentsConfig{
+			Defaults: config.AgentDefaults{
+				Workspace:         tmpDir,
+				ModelName:         "test-model",
+				MaxTokens:         4096,
+				MaxToolIterations: 10,
+			},
+		},
+	}
+	msgBus := bus.NewMessageBus()
+	provider := &recordingProvider{}
+	al := NewAgentLoop(cfg, msgBus, provider)
+
+	if _, err := al.ProcessDirectWithChannel(
+		context.Background(), "scheduled task", "agent:main:cli:direct:cron", "cli", "direct",
+	); err != nil {
+		t.Fatalf("ProcessDirectWithChannel(): %v", err)
+	}
+
+	if len(provider.lastMessages) == 0 {
+		t.Fatal("provider received no messages")
+	}
+	last := provider.lastMessages[len(provider.lastMessages)-1]
+	if last.Name != "" {
+		t.Errorf("last.Name = %q, want empty for cron-triggered message", last.Name)
+	}
+}
+
 func TestProcessMessage_UseCommandLoadsRequestedSkill(t *testing.T) {
 	tmpDir := t.TempDir()
 	skillDir := filepath.Join(tmpDir, "skills", "shell")
diff --git a/pkg/agent/context.go b/pkg/agent/context.go
index ecde7c33e..c6b4a1e2a 100644
--- a/pkg/agent/context.go
+++ b/pkg/agent/context.go
@@ -806,7 +806,7 @@ func (cb *ContextBuilder) BuildMessagesFromPrompt(req PromptBuildRequest) []prov
 	// multimodal providers receive the uploaded image even when the user sends
 	// no accompanying text.
 	if strings.TrimSpace(req.CurrentMessage) != "" || len(req.Media) > 0 {
-		messages = append(messages, userPromptMessage(req.CurrentMessage, req.Media))
+		messages = append(messages, userPromptMessage(req.CurrentMessage, req.Media, req.SenderID))
 	}
 
 	return messages
diff --git a/pkg/agent/pipeline_setup.go b/pkg/agent/pipeline_setup.go
index 219e4e5de..fa6dff530 100644
--- a/pkg/agent/pipeline_setup.go
+++ b/pkg/agent/pipeline_setup.go
@@ -69,12 +69,11 @@ func (p *Pipeline) SetupTurn(ctx context.Context, ts *turnState) (*turnExecution
 	}
 
 	if !ts.opts.NoHistory && (strings.TrimSpace(ts.userMessage) != "" || len(ts.media) > 0) {
-		rootMsg := userPromptMessage(ts.userMessage, ts.media)
-		if len(rootMsg.Media) > 0 {
-			ts.agent.Sessions.AddFullMessage(ts.sessionKey, rootMsg)
-		} else {
-			ts.agent.Sessions.AddMessage(ts.sessionKey, rootMsg.Role, rootMsg.Content)
-		}
+		rootMsg := userPromptMessage(ts.userMessage, ts.media, ts.opts.Dispatch.SenderID())
+		// AddFullMessage preserves all message fields (Name, Media, etc.).
+		// AddMessage(role, content) would silently drop Name attribution,
+		// breaking multi-user history disambiguation.
+		ts.agent.Sessions.AddFullMessage(ts.sessionKey, rootMsg)
 		ts.recordPersistedMessage(rootMsg)
 		ts.ingestMessage(ctx, p.al, rootMsg)
 	}
diff --git a/pkg/agent/prompt_turn.go b/pkg/agent/prompt_turn.go
index 588a8f00f..578d97ea5 100644
--- a/pkg/agent/prompt_turn.go
+++ b/pkg/agent/prompt_turn.go
@@ -5,6 +5,7 @@ import (
 	"strings"
 
 	"github.com/sipeed/picoclaw/pkg/providers"
+	"github.com/sipeed/picoclaw/pkg/providers/messageutil"
 )
 
 func promptBuildRequestForTurn(
@@ -95,11 +96,20 @@ func promptMessageWithDefaultMetadata(
 	return promptMessageWithMetadata(msg, layer, slot, source)
 }
 
-func userPromptMessage(content string, media []string) providers.Message {
+// userPromptMessage builds the per-turn user message that gets persisted
+// to session history and sent to the LLM. senderID is the raw inbound
+// sender ID; it is sanitized into the OpenAI-compatible Name field unless
+// it identifies a system trigger (cron, heartbeat, async callback), in
+// which case Name is left empty so synthetic events do not appear as
+// distinct human users in the conversation.
+func userPromptMessage(content string, media []string, senderID string) providers.Message {
 	msg := providers.Message{
 		Role:    "user",
 		Content: content,
 	}
+	if !messageutil.IsSystemSenderID(senderID) {
+		msg.Name = messageutil.SanitizeMessageName(senderID)
+	}
 	if len(media) > 0 {
 		msg.Media = append([]string(nil), media...)
 	}
diff --git a/pkg/agent/prompt_turn_test.go b/pkg/agent/prompt_turn_test.go
new file mode 100644
index 000000000..f043d519a
--- /dev/null
+++ b/pkg/agent/prompt_turn_test.go
@@ -0,0 +1,83 @@
+// PicoClaw - Ultra-lightweight personal AI agent
+// License: MIT
+//
+// Copyright (c) 2026 PicoClaw contributors
+
+package agent
+
+import (
+	"testing"
+)
+
+// TestUserPromptMessage_AttachesSanitizedSenderName verifies that
+// userPromptMessage stores a sanitized sender attribution in
+// providers.Message.Name when given a real human sender. This is the
+// core wiring change for issue #2702.
+func TestUserPromptMessage_AttachesSanitizedSenderName(t *testing.T) {
+	tests := []struct {
+		name     string
+		senderID string
+		wantName string
+	}{
+		{"slack-style id", "U07AB12C3DEF", "U07AB12C3DEF"},
+		{"discord-style id sanitized", "alice#1234", "alice_1234"},
+		{"telegram numeric", "141455495", "141455495"},
+		{"unicode display becomes empty", "李华", ""},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			msg := userPromptMessage("hello", nil, tt.senderID)
+			if msg.Role != "user" {
+				t.Errorf("Role = %q, want user", msg.Role)
+			}
+			if msg.Content != "hello" {
+				t.Errorf("Content = %q, want hello", msg.Content)
+			}
+			if msg.Name != tt.wantName {
+				t.Errorf("Name = %q, want %q", msg.Name, tt.wantName)
+			}
+		})
+	}
+}
+
+// TestUserPromptMessage_SkipsAttributionForSystemSenders verifies that
+// synthetic trigger sources (cron, heartbeat, async callbacks) do not
+// produce per-message attribution. These are not distinct human users,
+// so leaking them into Name would create spurious "user identities" in
+// the OpenAI wire format and a confusing `[cron] [System: ...]` double
+// prefix on Anthropic-style adapters.
+func TestUserPromptMessage_SkipsAttributionForSystemSenders(t *testing.T) {
+	systemIDs := []string{"", "cron", "heartbeat", "system", "async:read_file"}
+	for _, id := range systemIDs {
+		t.Run(id, func(t *testing.T) {
+			msg := userPromptMessage("triggered work", nil, id)
+			if msg.Name != "" {
+				t.Errorf("Name = %q, want empty for synthetic sender %q", msg.Name, id)
+			}
+		})
+	}
+}
+
+// TestUserPromptMessage_NoNameMeansNoAttribution covers the empty-sender
+// path explicitly so future refactors don't accidentally start tagging
+// anonymous direct-channel turns.
+func TestUserPromptMessage_NoNameMeansNoAttribution(t *testing.T) {
+	msg := userPromptMessage("anonymous message", nil, "")
+	if msg.Name != "" {
+		t.Errorf("Name = %q, want empty for anonymous sender", msg.Name)
+	}
+}
+
+// TestUserPromptMessage_PreservesMedia is a regression guard: the
+// existing media-passthrough behavior must continue to work after the
+// signature change.
+func TestUserPromptMessage_PreservesMedia(t *testing.T) {
+	media := []string{"data:image/png;base64,abc"}
+	msg := userPromptMessage("look", media, "alice")
+	if len(msg.Media) != 1 || msg.Media[0] != media[0] {
+		t.Errorf("Media = %v, want %v", msg.Media, media)
+	}
+	if msg.Name != "alice" {
+		t.Errorf("Name = %q, want alice", msg.Name)
+	}
+}